1. Field of the Invention
The present invention relates, in general, to implementing mismatched impedance components within data processing systems.
2. Description of the Related Art
Data processing systems are systems that manipulate, process, and store data and are notorious within the art. Personal computer systems, and their associated subsystems, constitute well known examples of data processing systems.
Personal computer systems typically include a main printed circuit board (xe2x80x9cmotherboardxe2x80x9d) for mounting at least one microprocessor and other application specific integrated circuits (ASICs), such as memory controllers, input/output (I/O) controllers, and the like. Most motherboards include slots for additional adapter cards (e.g., xe2x80x9cdaughter boardsxe2x80x9d) to provide additional function to the computer system. Typical functions that a user might add to a computer include additional microprocessors, additional memory, fax/modem capability, sound cards, graphics cards, or the like. The slots included on the motherboard generally include in-line electrical connectors having electrically conductive connector wipers which receive exposed fingerpads on the adapter cards. The connector wipers are connected to conductive vias, which in turn are connected to metallic traces on the printed circuit board which allow the components on the cards (e.g., memory modules) to communicate with one or more microprocessors or other components in the system.
A data processing system may include many different types of buses to link the various components of the system. Such buses are conventionally implemented as metallic traces on printed circuit boards.
In conventional data processing system design, it is typical to utilize various xe2x80x9coff the shelfxe2x80x9d components from one or more vendors in order to implement a data processing system. It has long been assumed in the data processing system art that it is preferable for such xe2x80x9coff the shelf componentsxe2x80x9d to have essentially the same xe2x80x9cTheveninxe2x80x9d equivalent impedances, because in classical circuit theory, conventionally used in data processing system design, matching Thevenin impedances of interconnected components are conventionally understood to allow for maximum power transfer and hence the greatest efficiency. In light of the foregoing, by a process of evolution, a de facto xe2x80x9cstandardxe2x80x9d has arisen within the data processing system art in which the impedances of various data processing system components, such as printed circuit board components, which interface and interconnect with various other data processing system components, generally have a characteristic impedance of roughly 60 ohms.
The emergence of this de facto xe2x80x9cstandardxe2x80x9d of roughly 60 ohms historically freed data processing system designers to innovate. That is, so long as the data processing system component designers ensured that the characteristic impedance of whatever component those designers were designing was roughly equal to 60 ohms, those designers could rely on the assumption that their so-designed components were electrically compatible with the rest of the data processing system. For example, computer memory module designers have long designed their computer memory modules to have characteristic impedances of roughly 60 ohms.
Relatively recently, engineers at the RAMBUS corporation, in an effort to get increased speed and efficiency in computer memory, decided to ignore the long-standing industry tradition of creating data processing system components which have characteristic impedances of 60 ohms. Instead, these designers chose to design their computer memory modules with 28 ohm characteristic impedances. In support of their memory modules, the RAMBUS corporation specified a printed circuit board connector which has a 28 ohm characteristic impedance.
A specification for a printed circuit board connector, entitled Direct RAMBUS(trademark) RIMM(trademark) Connector Specification, Rev. 1.01 by the RAMBUS Corporation (the xe2x80x9cConnector Specificationxe2x80x9d) is directed toward a small connector with relatively few components. Due to the speed and popularity of RAMBUS memory modules, desktop workstation data processing system designers have begun to design their systems to utilize RAMBUS memory modules. Unfortunately, when the inventors herein named (hereinafter, xe2x80x9cthe inventorsxe2x80x9d) have tried to implement these desktop system designs, the inventors have found that the Connector Specification printed circuit board connector (composed of a RAMBUS socket and a RAMBUS board edge connector) is too physically weak to work well in a desktop system environment. For example, in certain desktop workstation designs, it is common to mount relatively large numbers of memory modules on xe2x80x9criserxe2x80x9d boards (daughter boards which extend in a vertical plane relative to the motherboard) which are then affixed to the motherboard via printed circuit board connectors. The inventors have found that when such desktop workstations designs are implemented, the Connector Specification printed circuit board connectors are unable to adequately support the mechanical stresses associated with the rise cards, and tend to give rise to signal integrity and reliability problems owing to either the breaking or flexing of the Connector Specification printed circuit board connectors under the mechanical strain produced by the riser card.
In an effort to solve the foregoing noted problems, the inventors have tried to replace the Connector Specification printed circuit board connectors with more physically sturdy non-Connector Specification printed circuit board connectors (e.g., PCI specification connectors). In so doing, the inventors, using conventional circuit design techniques, concluded that even though the non-Connector Specification connectors did not match the 28 ohm impedance of the transmission lines of RAMBUS memory modules used in the Connector Specification, there would still be enough power transferred such that the loss of efficiency arising from the mismatched impedances would be outweighed by the increased accuracy arising from the superior mechanical strengths of the non-Connector Specification printed circuit board connectors.
Unfortunately, and unexpectedly, the inventors have found that when the non-Connector Specification connectors are implemented in RAMBUS systems, the performance of the RAMBUS memory modules becomes severely unacceptable. That is, the inventors have found that when the non-Connector Specification printed circuit board connectors are actually implemented in conjunction with RAMBUS memory modules, the errors associated with such modules are far below acceptable limits.
Insofar as conventional printed circuit board design techniques indicate that the mismatched impedance components should work together in an acceptable manner, the failure of the components to work together has given rise to a need for the inventors (1) to determine why the unacceptable errors are occurring, and, (2) if the cause of the unacceptable errors can be determined, to provide a method and system which will provide the ability to implement the non-Connector Specification connectors in RAMBUS systems in such a fashion that the performance of the systems is acceptable.
The inventors named herein have discovered at least one method and at least one related computer system that allow mismatched impedance data processing system components to be implemented such that the mismatched impedance data processing system components provide acceptable service in a data processing system. In one embodiment, the method includes but is not limited to exciting a printed circuit board circuit having mismatched impedance printed circuit board components, measuring at least one impedance of the circuit with a time domain reflectometer, and adjusting at least one printed circuit board circuit element, in response to the measured at least one impedance of the circuit. In one embodiment, the related computer system includes but is not limited to one or more printed circuit boards having at least one circuit wherein reside substantially mismatched impedance printed circuit board components, an impedance-variation equalizing distribution of at least one printed circuit board element operably coupled with the substantially mismatched impedance printed circuit board components, and said one or more printed circuit boards operably connecting at least one processor and at least one memory.
The foregoing is a summary and thus contains, by necessity, simplifications, generalizations and omissions of detail; consequently, those skilled in the art will appreciate that the summary is illustrative only and is not intended to be in any way limiting. Other aspects, inventive features, and advantages of the present invention, as defined solely by the claims, will become apparent in the non-limiting detailed description set forth below.